Pushing apparatus



Sepf- `1, 1964 J. MONTAGINO 3,146,879

PUSHING APPARATUS Fil'edv-Oct. 17, 1952 2 Sheets-Sheet 1 E E LIi'gfsfjp MUNTAAINU.

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United States Patent 3,146,879 PUSHING APPARATUS Joseph Montagino, Toiedo, (Ehio, assigner to Midland- Ross Corporation, Toledo, (Ehio, a corporation of hio Filed Get. 17, 1962, Ser No. 231,224 2 Claims. (Cl. 193-221) This invention relates to pushing apparatus particularly well suited to advance a series of trays along skid rails in an industrial heating furnace. More particularly, the invention relates to pneumatically operated pushing ap- .paratus of the aforesaid class wherein reciprocating linear motion is actuated by means of a nut on an elongate screw rotated to and fro.

Many users of industrial furnaces prefer that the operation of allthe various furnace components, such as doors, pushers, extractors, and the like, be pneumatically operated. Pneumatically operated motors and cylinders of conventional design have proven satisfactory for most appliactions. However, in furnaces of the type having a hearth formed of skid rails, wherein a plurality of workiilled trays in one of a plurality of rows thereof are advanced through the furnace in a sliding manner by a single pushing device, the pneumatic means heretofore available for actuating the pushing device have not been satisfactory. Conventional pneumatically operated cylinders, applied in the manner that conventional hydraulic cylinders are sometimes applied in similar situations, would behave erratically under the loadings involved which usually comprise at least a ton of components being simultaneously advanced by skidding at a coeiicient of friction approaching unity.

Pushing devices attached to a nut on an elongated screw rotated by a pneumatically driven motor have heretofore been used in such situations. However, the specific embodiments thereof have been relatively costly and have been of such an inherent width as to completely preclude their application to furnaces for processing closely spaced rows of narrow work-filled fixtures, which comprise a substantial fraction of the commerce in pusher type skid rail furnaces.

Therefore, it is the object of this invention to provide improved pushing apparatus of the screw pusher type. It is a further object of this invention to provide an improved pusher for an industrial furnace wherein the reciprocation of the pusher is actuated by a nut on a pneumatically rotated screw. It is a further object of the invention to provide a pneumatically operated industrial furnace screw pusher mechanism which can be constructed at less expense than the devices heretofore available. It is a further object of the invention to provide an industrial furnace screw pusher mechanism of less inherent width than prior art screw pusher mechanisms whereby to permit application of screw pusher mechanisms to pusher type furnaces for processing closely spaced rows of narrow work-filled trays. For other objects of the invention and for a further consideration of what is considered to be novel and inventive attention is directed to the following portion of the specification, the drawing, and the appended claims.

In the drawing:

FIG. l is an elevational view of the preferred embodiment of the invention shown in relationship with an associated furnace of the skid rail hearth type;

FIG. 2 is a plan view of the pusher of FIG. l at an enlarged scale and omitting details of the associated furnace;

FIG. 3 is a sectional view at a further enlarged scale taken on line 3 3 of FIG. 2, except that a portion of the apparatus is omitted as indicated by broken lines;

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FIG. 4 is a sectional view at a further enlarged scale taken on line 4 4 of FIG. 3;

FIG. 5 is a sectional view at an enlarged scale taken on line 5 5 of FIG. 2;

FIG. 6 is a fragmentary plan view of another embodiment of the invention; and- FIG. 7 is a sectional View taken on line 7 7 of FIG. 6.

In FIG. 1 a pusher mechanism shown generally at Il is illustrated as being mounted on a suitable framework 12 disposed in front of a furnace I3 having a hearth constructed of skid rails 14 along which work-filled trays W, indicated by discontinuous lines, are intermittently advanced by virtue of periodic reciprocation of pusher head portion 15 of pusher Il in a manner hereinafter described. To minimize the length of furnace required to operate at a given production rate it is customary to arrange trays W in a plurality of rows, each of which, preferably, is provided with a separate pusher 11. Further it is desirable that the clearance between adjacent rows be small and therefore, it is desirable that pusher Il be as narrow as possible, at least when the furnace is designed to accommodate narrow trays W, so that the spacing of adjacent pushers Il not exceed that required for the spacing of the respective adjacent rows of trays.

The furnace design concept utilizing a skid rail hearth along which work-filled trays are advanced by sliding is one frequently employed in continuous gas carburizing furnaces wherein a gaseous treating atmosphere of a predetermined relatively critical chemical composition is maintained. Thus, furnace 13 is heated indirectly by radiant elements, such as fuel fired radiant tubes 16, and is provided with a vestibule I7 separated from the main chamber of furnace 13 by retractable door I9 in customary fashion. Means, not shown, are provided to add fresh work filled trays to vestibule 17 from the side prior to each reciprocation of pusher head 15. Thus, when pusher head l5 is advanced it will first contact the work filled tray most recently added to vestibule 17 and will advance this new tray past the door station into the furnace until this tray contacts the last tray in the respective row after which pusher head 15 will continue to advance a distance approximately equal to the length of a single tray, thereby advancing each tray in the row by a distance approximately equal to one tray length. In practice, the stroke required of pusher head 15, which is the length difference between its retracted position, shown in solid lines, and its advanced position, shown in discontinuous lines, will be of the order of magnitude of 48 to 84 inches.

Pusher mechanism 1I, per se, comprises a very long screw 2t) with a threaded portion 21 and front bearing portion 22 mounted in thrust bearing 23, with a shoulder portion drawn up tight thereagainst by nut 24 threaded on the extremity of screw 20. Bearing 23 is mounted in a housing 25 which is attached to forward mounting bracket 26 which, in turn, is bolted to framework 12. Screw 2t) is also provided with a rear bearing portion 27 which is mounted in non-thrust bearing 2S which, in turn, is connected to framework 12 by means of rearward mounting bracket 29.

Threaded onto threaded portion 21 of screw 2t) is an internally threaded nut 31 which, if suitable means are provided to restrain the rotation thereof in a manner hereinafter described, will be caused to travel to and fro in a linear direction by forward and backward rotation of screw 2i).

The rotation of screw 20 is pneumatically operated by means of pneumatic motor 32 mounted on framework I2 and coupled to drive sheave 33 by means of a V-belt 34. It is characteristic of such a drive arrangement that the torque build-up is relatively slow and it is desirable, therefore, to minimize the resisting torque arising in the form of friction between nut 2S and threaded portion 21 by using a nut and screw assembly of the ball bearing type, as illustrated, items commercially available from Saginaw Steering Gear Division of General Motors Corporation.

Pusher head portion of pusher 11 is preferably of a width approaching the width of the trays to be pushed for uniform application of the pushing forces. To minimize bending forces on a pusher head of such width it is desirable that the pushing force imparted thereto be done so at two spaced apart points. Therefore, pushing force from reciprocating nut 31 is, ultimately, delivered to pusher head 15 by means of two elongated spaced apart pusher rods 35. The forward end of each pusher rod 35 is secured to pusher head 15 and support is furnished for each pusher rod as it reciprocates by means of a bushing 36 secured to forward mounting bracket 26, as shown in some detail in FIG. 5.

As shown in FIG. 2, the rearward end of each pusher rod 35 is provided with a necked down portion 37 forming an annular shoulder 38. The necked down portion 37 of each pusher rod 35 is passed through an appropriately located hole in a crosshead member 40 and annular shoulder 33 of rod 35 is drawn up tight against a matching face 41 of crosshead member 40 by a nut 42 threaded on the end thereof. Crosshead member 40 further cornprises an annular fiange 43 which attaches to fiange adapter portion 44 of ball nut 31.

Because of the various forces and couples acting on crosshead 4t) it is necessary to provide guide means to properly guide its travel as it reciprocates to and fro when screw is rotated one way and then the other. Because of the requirement that pusher 11 be compact in width, it is important that the guide means act on crosshead 40 at points within the lateral clearance between pusher bars 35. It has been found that an elongated casing closely circumposing a substantial portion of the rotating screw and being provided with at least one slot through which the crosshead passes as it extends from the nut constitutes excellent guide means. Thus, in the embodiment of FIGS. 1-5, wherein crosshead 4f) comprises a single horizontally disposed plate extending from one pusher bar to the other, there is provided a casing 45 comprising, in its simplest form, a long metal tube circumposing threaded portion 21 of screw 20 and having a horizontal slot 46 on each side thereof extending forward from the rear extremity thereof for a substantial distance, as determined by the stroke required of pusher head 15. Crosshead is provided with a milled slot 47 on the top and bottom of each side thereof at the point where it emerges from the interior of casing 45. Slots 47 are of such a depth as to leave sufficient material to form a suitable running fit in slot 46.

In the embodiment of FIGS. 6 and 7, components which may be the same as components in the embodiment of FIGS. 15 are denoted by like reference numerals and components which need differ in construction are denoted by a 100 series reference numeral the last two digits of which correspond to the digits of the reference numeral of a component serving an analogous function, if any, in the embodiment of FIGS. 1-5. According to this embodiment there is provided a crosshead 140 of composite construction for transmitting linear motion from ball nut 31 to pusher rods 35. Crosshead 140 comprises an elongate pushing finger 151 attached to annular flange 43 and extends, preferably vertically, from casing 145 through a single guide slot 146 therein. Securely attached to pushing finger 151 and closely circumposing casing 145 in such a manner as to form a close moving fit therewith is a sleeve 152 of moderate length. The close fit between sleeve 152 and casing 145 serves to provide a turning couple which offsets the turning couple which would otherwise be imposed on screw 20 when, unlike the embodiment of FIGS. 1-5, nut 31 is eccentrically loaded.

Each of pusher rods 35 is affixed to sleeve portion 152 of crosshead by means of a mounting bar 153, which is attached to the exterior of sleeve portion 152 in a manner similar to the mode of attachment to crosshead 40. Thus, the embodiment of FIGS. 6 and 7 requires a crosshead 149 of somewhat more complex construction than crosshead 4) of the embodiment of FIGS. 1-5. To some extent, however, this advantage in favor of the embodiment of FIGS. 1-5 is offset by virtue of the fact that casing of the embodiment of FIGS. 6 and 7 need be provided with only a single elongate slot 146 whereas casing 45 requires a pair of slots 46.

It has heretofore been mentioned that the bearing 23, which receives the forward bearing portion 22 of screw 20, is adapted to sustain thrust along the axis of screw 20. The advantage of locating the thrust bearing at the forward end of screw 20 rather than at the rearward end is that the resultant axial force on the portion of the screw between nut 31 and the thrust bearing during the forward stroke of crosshead 15 is tensile rather than compressive thereby obviating the need for considering column effects in the design of screw 20.

As will be evident to those skilled in the art, various modifications and alternatives can be made to the embodiments of this invention without departing from the spirit or scope of the disclosure or the claims.

I claim:

l. Pushing apparatus comprising, in combination: a long screw; bearing means for mounting the screw; drive means comprising a pneumatic motor for rotating the screw in one direction and then in the other; a nut threaded onto the screw and adapted to move linearly to and fro as the screw is rotated in one direction and then in the other; casing means circumposing at least a portion of the screw and forming a slot whose axis extends parallel to the axis of the screw; a crosshead attached to the nut and adapted to move linearly therewith and comprising a portion extending outwardly from the nut through the slot; a sleeve attached to the portion of the crosshead extending through the slot, said sleeve circumposing the casing means and forming a close moving fit therewith; pusher head means; a first long rod having one end operatively afiixed to the sleeve and the other end attached to the pusher head means; and a second long rod spaced apart from the first long rod, extending generally parallel thereto, having one end operatively fixed to the sleeve, and having the other end attached to the pusher head means.

2. Apparatus according to claim 1 wherein the exterior of the casing means and the interior of the sleeve are generally circular and wherein the axial length of the sleeve is substantial in relation to diameter of the interior of the sleeve. 

1. PUSHING APPARATUS COMPRISING, IN COMBINATION: A LONG SCREW; BEARING MEANS FOR MOUNTING THE SCREW; DRIVE MEANS COMPRISING A PNEUMATIC MOTOR FOR ROTATING THE SCREW IN ONE DIRECTION AND THEN IN THE OTHER; A NUT THREADED ONTO THE SCREW AND ADAPTED TO MOVE LINEARLY TO AND FRO AS THE SCREW IS ROTATED IN ONE DIRECTION AND THEN IN THE OTHER; CASING MEANS CIRCUMPOSING AT LEAST A PORTION OF THE SCREW AND FORMING A SLOT WHOSE AXIS EXTENDS PARALLEL TO THE AXIS OF THE SCREW; A CROSSHEAD ATTACHED TO THE NUT AND ADAPTED TO MOVE LINEARLY THEREWITH AND COMPRISING A PORTION EXTENDING OUTWARDLY FROM THE NUT THROUGH THE SLOT; A SLEEVE ATTACHED TO THE PORTION OF THE CROSSHEAD EXTENDING THROUGH THE SLOT, SAID SLEEVE CIRCUMPOSING THE CASING MEANS AND FORMING A CLOSE MOVING FIT THEREWITH; PUSHER HEAD MEANS; A FIRST LONG ROD HAVING ONE END OPERATIVELY AFFIXED TO THE SLEEVE AND THE OTHER END ATTACHED TO THE PUSHER HEAD MEANS; AND A SECOND LONG ROD SPACED APART FROM THE FIRST LONG ROD, EXTENDING GENERALLY PARALLEL THERETO, HAVING ONE END OPERATIVELY FIXED TO THE SLEEVE, AND HAVING THE OTHER END ATTACHED TO THE PUSHER HEAD MEANS. 